With the continual scaling of feature size and the ever-expanding functionalities of chips, sizes of wires that connect components in a chip are also reduced, causing current densities through the wires to increase. A life span of a wire is subject to electromigration, which is a material transport caused by transfer of momentum between conducting electrons and metal ions. Electromigration can cause the formation of hillocks or voids in the wire, which can lead to short circuit or open circuit. A mean time to failure (MTTF) of the wire, when estimated taking electromigration into consideration, decreases with the increase of current density.